4,6-diaminopyrimido[5,4-d]pyrimidines are known for example from WO 97/32880 and are valuable pharmaceutical compositions which have, in particular, an inhibitory effect on signal transduction mediated by tyrosine kinases.
However, the method of preparation described therein is unsuitable for production on an industrial scale as the desired products are described as being obtained from starting materials which are not easily accessible, such as 4-anilino-6-methylsulphinyl-pyrimido[5,4-d]pyrimidines or 4-anilino-6-methylsulphonylpyrimido[5,4-d]pyrimidines which, when reacted, give off foul-smelling and toxic thiols which lead to contamination of the products.
The aim of the present invention is therefore to provide a process which makes it possible to synthesise, work up, purify and isolate 4,6-diaminopyrimido[5,4-d]pyrimidines of formula I on an industrial scale while overcoming the disadvantages mentioned above.